High voltage power lines transmit electrical power over long distances. A conventional high voltage transmission line utilizes three spaced apart, side-by side phases of conductors, each phase comprising one or more electrical conductors. Where more than one conductor is used in a phase, the conductors comprise a bundle of conductors which are generally supported parallel to one another. In one typical arrangement, each phase comprises a bundle of three triangularly arranged conductors in which two upper conductors are in the same horizontal plane and the third conductor is in a lower horizontal plane but is positioned centrally between the two upper conductors. It will be appreciated, however, that each phase can comprise a single conductor, two parallel conductors, or multiple conductors per bundle.
These high voltage power lines are generally supported by vertical support structures which vary in height between conventional wooden poles having upper cross bars to extremely tall towers which may be several hundred feet in height. The support structures extend upwardly from the ground and are, therefore, electrically grounded. As a consequence, the very high voltage, energized electrical power line conductors are supported on the towers by insulator strings, which frequently comprise a series of porcelain covered discs interconnected to form strings of varying length, in order to prevent the high voltage power line conductors from arcing to the grounded support towers.
In many instances, due to the height of the power lines above the ground or the terrain, maintenance and repair of high voltage electrical power lines cannot be accomplished from trucks. It has been known for years to do maintenance and repair on power lines using a helicopter to lift service personnel to the power lines. For example, one technique involves suspending a “bucket” housing in which a lineman can work from a helicopter alongside electrical power lines to allow the lineman to do work on the electrical power lines. More recently, work on power lines has been done by linemen seated on platforms suspended under helicopters which hover adjacent the power lines. This has worked well on the outer phases of three phase arrangements since bundles in these phases are readily accessible from helicopter-mounted platforms. However, more recently, due to federal, state and/or power company regulations, due to arcing concerns helicopters are no longer permitted to hover between phases and, therefore, the middle phase is no longer accessible to helicopter-mounted platforms. In order to access the middle phase of a three phase conductor arrangement, carts or skips have been developed which comprise generally rectangular, perforated metal or tubular enclosures or baskets suitable for housing a lineman and which include horizontal support frames above the enclosures or baskets having wheels or rollers for supporting the cart or skip upon one, two or more power line conductors. Illustrative skips are disclosed in U.S. Pat. Nos. 3,702,124, 4,163,480 and 4,478,312. Working from one of these carts allows the lineman to work on the middle phase conductor bundle. Some of these carts or skips are motorized and are able to self-propel along the lines. In many instances these carts are initially emplaced upon the power lines by ground-based cranes or are otherwise hoisted onto the power lines. More recently, helicopters have been used.
As is well known, high voltage power line conductors hang in catenaries between support towers, which may be a considerable distance apart. Thus, the conductors incline downward from a first support tower, have a reduced incline toward the center of the span between towers and incline upward as they approach the second support tower. Particularly where the span between support towers is long, the towers may be very tall. However, the vertical support structures which support the power line conductors as they approach the first tall tower of the span and as they leave the second tall tower of the span are generally considerably shorter. It will be appreciated, then, that the power line conductors extend from the last of the shorter approach towers to the top of the first tall tower at a very steep incline and, on the other side of the span, the power line conductors extend from the top of the second tall tower down to the first of the shorter towers at a very steep decline. A cart traveling along these power line conductors must be able to move up and down and along these steep inclines, and to service the power lines along these inclines, either under its own motive power or as a result of being raised or lowered by a towing device, such as a winch and cable.
Accordingly, there is a need for a cart for servicing energized electrical power lines which can be safely emplaced on and travel along at least two parallel electrical power lines, which can negotiate the steep inclines which may be encountered in moving along the lines, frequently under their own power, and which supports at least one lineman in close proximity to the electrical power lines to be serviced.